1. Field of the Invention
The present invention relates to an electric power steering apparatus and a control method thereof and, more specifically, to an electric power steering apparatus and a control method that can determine whether a driver keeps hold of a steering wheel.
2. Description of the Prior Art
In general, vehicles have auxiliary steering systems as a means for reducing a steering force of a steering wheel to ensure stability of a steering state. In the related art, Hydraulic Power Steering Systems (HPSs) using hydraulic pressure have been widely used as auxiliary steering systems for vehicles. However, these days, eco-friendly Electric Power Steering Systems (EPSs), which reduce a steering force using a rotating force of a motor as opposed to the related art using hydraulic pressure, are usually equipped to vehicles in order to enable drivers to easily steer their vehicles.
In the electric power steering systems (EPSs), Electronic Control Units (ECUs) drive motors according to driving conditions of vehicles, which are detected by vehicle speed sensors, steering angle sensors, torque sensors, etc., to provide a light and convenient feeling of steering at a low speed and good directional stability as well as a heavy feeling of steering at a high speed and to provide a rapid restoring force according to rotation angles of steering wheels so that rapid steering can be performed in an emergency situation, thereby providing optimum steering conditions to drivers.
Meanwhile, among various types of technologies that are added in order to ensure driving stability, lane keeping control systems have been increasingly used to prevent lane departure caused by drivers' drowsy or careless driving.
Lane keeping control systems control actuators of steering control systems by using lane information (e.g., the location, width, curvature, or the like of a lane), which is acquired through cameras, to assist drivers to drive their vehicles while stably keeping lanes. Examples of the lane keeping control systems include a Lane Keeping Assist System (LKAS), a lane keeping system, a lane departure prevention system, and the like.
The roles of such lane keeping control systems are limited to a function of providing assist torques in order to make drivers keep their lanes. Accordingly, in cases where drivers do not keep hold of steering wheels, it is required to make an alert by rapidly detecting dangerous situations due to the hands-off state of the steering wheels.
However, steering wheel hands-off detection technologies in the related art simply use torque values that are output from torque sensors, and thus, there may be a difference between the torque values and the actual torque levels acting on steering wheels.
Further, in the steering wheel hands-off detection technologies, a determination as to whether a driver does not keep hold of a steering wheel is made by simply comparing an output value of a torque sensor of a steering system with a threshold value. Therefore, an error in the determination may arise when a steering torque value temporarily varies according to a road condition, etc.